Process for manufacturing toothed belts of elastomeric material and toothed belt made by said process

ABSTRACT

In a process for manufacturing toothed belts of any length, a tubular sleeve comprising a layer of cords (1) and at least a layer of elastomeric material (2) is preformed in an autoclave without being vulcanized so as to produce, on the inner surface thereof, a plurality of grooves (5) spaced apart from one another according to a predetermined toothing pitch (P). The sleeve is helically cut to obtain a continuous strip (7) to be subsequently wrapped over two wrapping drums (8, 9) suitably spaced apart from each other depending on the circumferential extension to be given to the belt. The obtained annular element (10), when the wrapping has been completed, is trued up by means of the provided grooves, between a molding matrix (11) and opposite mould (12) and is submitted to a pressing step and simultaneous cross-linking of the elastomeric material (2) by closing said elastomeric material between the molding matrix (11) and opposite mold (12) according to stages in succession. Thus the complete formation of the teeth (3) on the inner side of the belt being worked occurs, as well as the firm bonding of the continuous loops (10a) formed by wrapping of the continuous strip (7).

REFERENCE TO RELATED APPLICATION

This application is a division of U.S. Ser. No. 07/983,171, filed Nov.11, 1992 which will issue on Jun. 6, 1995 as U.S. Pat. No. 5,421,927.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a process for manufacturing toothedbelts of elastomeric material, comprising the following steps: making asemifinished product in the form of a continuous strip; wrapping thesemifinished product in the form of a strip over at least two wrappingrollers having parallel axes and being spaced apart according to apredetermined distance between centers, said wrapping being carried outaccording to a wrapping pitch corresponding to the width of thesemifinished product in order to achieve an annular element of thedesired circumferential extension or length, of at least the same widthor axial length as the toothed belt to be achieved and formed with aplurality of loops disposed in mutual side-by-side relation.

The invention also relates to a toothed belt of elastomeric material ofthe type comprising: at least a layer of reinforcing cords of annularconfiguration; at least a layer of elastomeric material incorporatingsaid reinforcing layer and exhibiting, on an inner surface thereof, aplurality of teeth extending transversely to the circumferentialextension or length of the belt and spaced apart from each other by thesame distance, according to a predetermined toothing pitch.

2. Prior Art

It is known that toothed belts of elastomeric material consist of a bodyclosed in the form of a loop and are essentially comprised of a layer oflongitudinal reinforcing cords incorporated within at least a layer ofelastomeric material in which a plurality of shaped teeth, spaced apartfrom each other by the same distance according to a predeterminedtoothing pitch, are defined on the inner side of the circumferentialbelt extension.

The manufacture of these belts involves producing a tubular sleevehaving inner and outer circumferential surfaces which is obtained bysuccessively wrapping the layer of reinforcing cords and the layer ofelastomeric material in the raw state over a cylindrical drum havingaxially extending grooves or tooth spaces matching the shape of thetoothing to be achieved.

The sleeve disposed on the drum is then submitted to a simultaneousmolding and cross-linking process within an autoclave. In particular,the sleeve is submitted to a homogeneously applied pressure for apredetermined period of time. Thereafter the elastomeric material isurged into the axially extending grooves of the drum in order to causethe formation of teeth.

During this process, the overall processing time of which is notgenerally less than 15 minutes, the sleeve is submitted to hightemperatures, generally in the range of 150° to 170° C., in order tocause the complete cross-linking of the elastomeric material and,consequently, the structural stabilization of the obtained toothedsleeve.

As far as mass production is concerned, the circumferential extension orlength of the drum on which the sleeve is formed is normally coincidentwith the circumferential extension or length that the finished beltsmust have. In such cases it is sufficient to slit the sleeve accordingto several suitably axially spaced circumferentially-parallel lines inorder to obtain a plurality of belts having the desired circumferentialextension and axial width.

There are, however, many other cases in which the circumferentialextension of the drum, and consequently that of the obtained sleeve, issmaller than the circumferential extension that the finished belts musthave.

This occurs for example when it is necessary to produce belts of a givencircumferential extension in relatively small supplies, which does notjustify preparing drums of sizes selected for purposes of producing suchbelts. In other cases the circumferential extension of required beltsmay be so great that making drums of very large sizes is involved, solarge in fact that they cannot even be introduced into available factoryequipment, such as for example vulcanization and molding autoclaves, andgrinding and packaging machines.

In order to solve such problems, the sleeve obtained from the moldingand cross-linking process is slit according to a line of helicalextension, the pitch of which is coincident with the width of the beltsto be achieved. In this way a semifinished product in the form of acontinuous strip is produced which lends itself to be cut to sizeaccording to the circumferential extension of the desired belt which isthus obtained by joining end-to-end the opposite ends of the striplength cut to size.

By this method it is possible to produce toothed belts of anycircumferential extension, but it is necessary to accept the unavoidablestructural weakening of the belt caused by the end-to-end junctionpresent on the circumferential extension thereof.

U.S. Pat. No. 4,083,838 discloses a method by which it is possible toobtain belts of thermoplastic material in the desired length withoutend-to-end junctions of the above described type being required.

In accordance with this method, a semifinished product in the form of acontinuous strip, on which a toothing in its final configuration hasbeen previously produced, is passed over two rollers having parallelaxes, mutually positioned according to a distance between centerscorresponding to the desired circumferential extension to be given tothe obtained belt. The wrapping of the semifinished product is carriedout helically according to a pitch corresponding to the width of thesemifinished product so as to form a plurality of loops disposedconsecutively in side-by-side relation and mating at the respectiveopposite edges.

A heating means is provided close to one of the rollers on which thewrapping is carried out, said means, assisted by a presser ribbon guidedaccording to a determined wrapping arc about the roller, causing theplasticization of the thermoplastic material forming the semifinishedproduct, so that the loops disposed in side-by-side relation are firmlybonded to each other.

Thus an annular toothed element is produced that lends itself to be cutaccording to circumferential lines thereby giving rise to a plurality ofbelts having the desired width and circumferential extension.

Presently it is impossible to use the above method to make toothed beltsin which elastomeric material is used in place of the thermoplasticmaterial.

In fact, cross-linking carried out in the autoclave before thesemifinished product takes the form of a continuous belt would make thesubsequent melting of the elastomeric material for obtaining the mutualjunction between contiguous loops an impossible achievement.

In accordance with his own experience, the Applicant has conceived oflowering the temperature and residence times of the manufactured articlein the autoclave, in order to avoid cross-linking of the elastomericmaterial, which operation would have been executed in a subsequent step;however, it has been found that the formation of teeth on the innersurface of the sleeve did not take place in a regular manner, so that itwas impossible to resort to this procedure.

In accordance with the present invention it has been found that in orderto obtain toothed belts made of elastomeric material, of anycircumferential extension without mechanical junctions, it is possibleto resort to a process in which the above autoclaving step is used tofundamentally form the toothing pitch without cross-linking theelastomeric material. That is, intertooth spaces and teeth, theconfigurations of which only partly correspond to the finalconfiguration of the teeth are first produced, and, in a subsequentstep, cross-linking of grooves (and/or projections) is conducted byplacing the noncross-linked product between two mold members, andpressing the members together in the presence of heat to give the teeththeir ultimate shape and, by cross-linking of the elastomeric material,causing the contiguous loops of the annular element to adhere to eachother so as to form a belt of the desired length devoid of anymechanical junctions. In practice, a process is adopted in which asemifinished product, in the form of a continuous strip, is obtained byhelically cutting a sleeve that has been previously subjected in anautoclave to a preforming step which is not necessarily intended tocomplete construction of teeth but does form teeth and intertooth spacesor grooves according to the toothing pitch to be given to the belts,without, however, cross-linking the elastomeric material present in thesleeve. The semifinished product thus obtained in the form of acontinuous strip is then helically wrapped about two spaced apartrollers, which are spaced by a distance depending on the desired beltextension or length, in order to produce an endless ring the adjacentloops of which, as they are in the raw state, enable the cross-linkingof the elastomeric material to take place after the ring has been cut tothe desired width, which results in the production of a junction-freebelt. Intertooth spaces or grooves, obtained in the preforming operationare then used to true up the annular element obtained from the stripwrapping, on a matrix employed for molding and cross-linking the finaltoothing profile.

The present invention in one main aspect thereof relates to a processfor manufacturing toothed belts of elastomeric material comprising thefollowing steps: making a sleeve having circumferentially extendinginner and outer surfaces, the inner such surface having intertoothspaces and teeth; cutting the sleeve according to a cutting line ofhelical extension so as to obtain a semifinished product in the form ofa continuous strip; wrapping said semifinished product in the form of acontinuous strip over two spaced apart wrapping toothed rollers havingaxes parallel to one another and positioned according to a predetermineddistance measured from the centers of said axes, said wrapping beingcarried out at a pitch corresponding to the width of the semifinishedproduct in order to obtain an annular element of the desiredcircumferential extension having at least the same width as the toothedbelt to be produced and formed with a plurality of loops disposed inmutual side by side relation, characterized by:

a) controlling the temperature and time of the sleeve-making step so asto obtain a plurality of alternate intertooth spaces or grooves andteeth to preform the teeth defining the belt pitch while avoidingcross-linking the elastomeric material of the sleeve;

b) trueing up the annular element in the raw state, by means of saidintertooth spaces or teeth positioned between a molding matrix and anopposing mold member;

c) pressing the matrix and the mold toward each other to compress thesleeve and applying heat thereto to vulcanize the sleeve, so as to moldthe teeth to the final shape and cause the mutual bonding of theside-by-side loops of the annular element in the raw state, therebygiving rise to a belt of desired length, without mechanical junctions.

More particularly, this process is characterized in that the productionof the semifinished product in the form of a continuous strip takesplace through the following steps: a cylindrical tubular sleeve ismanufactured by wrapping at least a layer of textile reinforcing fibersand at least a layer of raw elastomeric material over a preforming drumwith substantially longitudinal teeth circumferentially distributedaccording to a predetermined toothing pitch; preforming the tubularsleeve by compressing the elastomeric material against the preformingdrum teeth so as to produce, on the inner circumferential surface ofsaid sleeve, a plurality of substantially longitudinal groovesdistributed according to said toothing pitch, associated with toothpreforming projections; cutting the tubular sleeve according to acutting line of helical extension, so as to obtain said semifinishedproduct in the form of a continuous strip of predetermined width havingtransverse grooves distributed according to said toothing pitch, aftersaid wrapping step the annular element provided with said transversehollows on an inner surface thereof being submitted to the steps of:pressing the annular element between a molding matrix and an opposingmold member which matrix and member act on the inner surface and anouter surface respectively of the annular element so as to define onsaid inner surface a plurality of shaped teeth spaced apart bytransverse grooves; cross-linking the elastomeric material present inthe annular element by administering heat thereto, in order to cause themutual bonding of said loops disposed in side-by-side relation duringthe wrapping step, as well as a structural stabilization of the obtainedtoothed belt.

Advantageously, during said pressing step a final mutual trueing of therespectively aligned transverse grooves belonging to the individualloops of the semifinished product previously wrapped in the form of astrip, is carried out.

During said wrapping step a mutual alignment of the transverse groovespresent in the individual loops of said semifinished product in the formof a strip is also preferably executed. This alignment is obtained byengagement of said grooves on longitudinal-alignment teeth provided onsaid wrapping rollers, which are spaced apart by the same distance assaid toothing pitch.

Preferably, in the production of the cylindrical tubular sleeve acoating fabric is first placed on the preforming drum before carryingout the wrapping of the textile fiber layer and the raw elastomericmaterial.

In addition, during said pressing step, a covering fabric previouslyinterposed between said molding matrix and the annular element may alsobe fastened to the inner surface of the annular element. The applicationof a covering fabric to the inner surface of the annular element can beexploited in order to execute a presetting of the loops of thesemifinished product in the form of a strip before the pressing step.

In this case said covering fabric is applied during said wrapping stepby positioning the covering fabric between the wrapping rollers and theannular element being worked.

Alternatively, the mutual presetting of the loops formed with saidsemifinished product can take place through application, after saidwrapping step, of an outer coating sheet to the outer surface of theannular element wrapped around said wrapping rollers.

The cross-linking step of the elastomeric material is preferablyobtained simultaneously with the pressing step, through heating of themolding matrix and opposite mold member. In addition, the pressing stepis carried out by successive stages to each of which the pressing of aportion of predetermined length of said annular element corresponds.

After the cross-linking step, the edges of the obtained toothed belt maybe trimmed.

In the case in which the annular element has an important width, it ispossible to execute a circumferential cutting step after saidcross-linking step, in order to obtain a plurality of toothed belts ofpredetermined width.

Alternatively, this circumferential cutting step can be executed beforethe pressing step.

In accordance with a further feature of the invention, the preformingstep is conducted so that the grooves on the sleeve exhibit a depthcorresponding to at least 1/3 of the height detectable on the individualteeth of the finished belt, and alternate with projections thetransverse preforming outline of which has a surface extension equal toat least 1/2 of the surface extension detectable on the tooth profile ofthe finished belt.

Preferably, in accordance with the process of the invention, after themolding step at least 10% of said projections should be only partlyformed as regards their detectable height and/or their sizes as abovedescribed.

More preferably at least 30% of the projections are partly formed asabove stated and still more preferably at least 50% of the projectionsare partly formed as above stated.

Advantageously the application of centripetal pressure during theforming step takes place concurrently with the administration of heat tothe sleeve being worked.

In greater detail, the application of centripetal pressure during thepreforming step is carried out in an autoclave concurrently with theadministration of heat to the sleeve over a period of time determined tobe between 1/6 and 1/2 of the time necessary to cause the completecross-linking of the elastomeric material at the temperature conditionsaccording to which the administration of heat occurs.

Alternatively, the administration of heat to the sleeve is carried outby submitting the latter to temperatures of a value included between 1/2and 4/5 of the value needed to obtain the complete cross-linking of theelastomeric material over a period of time corresponding to the durationof the administration of heat.

In a preferred embodiment, the application of pressure during apreforming step occurs at a value in a range of 10 bar to 22 bar, over aperiod of time of 2 to 15 minutes, while administering heat to thesleeve at a temperature in the range 50° C. to 205° C. at the outsidethereof, and in the range of 100° C. to 140° C. at the inside thereof,depending on fluid used (that is air, steam or pressurized water).

After the preforming step the material has not been subjected to avulcanization process and, hence, physical parameters of the vulcanizeditem such as hardness and ultimate tensile strength are not measurable.

The invention in another aspect thereof also relates to a toothed beltof elastomeric material obtained by the above process, said belt beingcharacterized in that said reinforcing cord layer, in the form of acontinuous strip, is helically wrapped in several loops disposed in aside-by-side relation and mated at the respective opposite edges.

Preferably, the belt further comprises at least a coating fabric appliedto the inner surface thereof provided with said teeth, said coatingfabric being structured in the form of a continuous strip wrapped inseveral side-by-side loops mating at the respective opposite edges.

The belt may also comprise at least a covering fabric, which is appliedto the inner surface thereof provided with teeth, said covering fabricbeing structured in the form of a continuous strip of the same width asthe belt.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages will become more apparent from thedetailed description of a preferred embodiment of a process formanufacturing toothed belts of elastomeric material and a belt obtainedby said process, in accordance with the present invention, givenhereinafter by way of non-limiting example with reference to theaccompanying drawings, in which:

FIG. 1a shows, by way of example only, a diagram indicating thevariations in time of the feed pressures in an autoclave for theexecution of a preforming step in accordance with the process of theinvention;

FIG. 1b shows a diagram similar to the diagram shown in FIG. 1a andrelates to pressure variations in the autoclave according to the moldingand cross-linking processes of the known art;

FIGS. 2a and 2b show diagrams obtained through the so-called "Monsantotests" carried out respectively on a coupon of elastomeric materialsubmitted to the preforming cycle in an autoclave and on a coupon of rawelastomeric material, of the same type, not submitted to said cycle;

FIG. 3 shows a diagrammatic perspective view of the execution of awrapping step of a semifinished product in the form of a continuousstrip over a pair of mutually spaced apart wrapping rollers;

FIG. 4 shows, in section, a side view of a portion of an annular elementdisposed between a matrix and an opposite mold and being submitted to afinal-molding and cross-linking step;

FIG. 5 diagrammatically shows the superimposition of the outlines of acompletely formed tooth (in dotted line) and a tooth not completelyformed (in solid line), respectively.

The process of the present invention relates to manufacturing drivingbelts of elastomeric material of the type essentially comprising atleast a layer of longitudinally extending reinforcing cords 1 made oftextile fibers, fiberglass (FIG. 4) or other materials such as aramidefibers or the like, as currently used in belts, incorporated within atleast a layer of elastomeric material 2 shaped such as to define, on theinner surface of the circumferential belt extension, a plurality ofshaped teeth 3 spaced apart from each other in a predetermined toothingpitch "P".

To this end, a cylindrical tubular sleeve having outer and innercircumferential surfaces is first made in a manner known per se bywrapping the reinforcing cord layer 1 and the elastomeric material layer2 in a raw state and in the form of a sheet of constant thickness abouta cylindrical preforming drum having on the surface thereof a pluralityof substantially longitudinal teeth spaced apart from each other adistance corresponding to the toothing pitch "P".

These operations are preferably preceded by the engagement on thepreforming drum of a tubular textile stock material designed to form aninner coating fabric 4 for the sleeve and hence the finished belts. Theinner coating fabric 4 not only strengthens the structure of theindividual teeth 3, but also makes the subsequent removal of the sleevefrom the drum easier.

The tubular sleeve together with the preforming drum on which it hasbeen formed, is then introduced into an autoclave of the type normallyused for molding and cross-linking sleeves in the production processesof the known art.

Inside this autoclave, which is not shown and which is known per se, thesleeve undergoes a preforming step to create, on the inner surface ofthe sleeve, a plurality of shaped grooves 5 spaced apart from each otherby a given toothing pitch "P" and alternated with surface projections3a, each of which will form one of said teeth 3.

The sleeve preforming step taking place in the autoclave is carried outby applying homogeneously distributed centripetal compression forces tothe sleeve in a known manner and which is described below, so that theelastomeric material 2 urged through the textile reinforcing layer 1 andagainst the longitudinal teeth of the drum will at least partly fill thegrooves on the drum defined by two adjacent teeth.

In order to increase the malleability of the elastomeric material 2,heat is simultaneously administered with centripetal compression to thesleeve being worked. However, the administration of heat and tiletreating time in the autoclave must be adjusted so that cross-linkingdoes not occur in the elastomeric material.

In order to accomplish this purpose, the residence time of the sleeve inthe autoclave and/or the treatment temperatures therein are convenientlyreduced as compared to those of the known art wherein the working cyclesachieve complete formation of teeth 3 and the simultaneous completecross-linking of the elastomeric material.

For an easier understanding, the graphs of FIG. 1a show, by way ofexample, the variations in time of the preforming treatment pressures inthe autoclave carried out in accordance with the invention on a sleeveof chloroprene-based elastomeric material having the followingcomposition:

    ______________________________________                                        Chloroprene          52.35%                                                   Magnesium oxide + zinc oxide                                                                       3.95%                                                    Silica + activators  11.8%                                                    Blacks               28.8%                                                    Antifatigue agents   1.55%                                                    Antiozone            1.55%                                                    ______________________________________                                    

It is pointed out that chloroprene is one example of the elastomericmaterials used; other elastomeric materials that could be used includepolybutadiene rubber-based materials, nitrile, hydrogenated andchlorosulfonated rubbers.

For purposes of comparison, the graph of FIG. 1b shows the developmentof pressures that can be found in the molding and cross-linking step ofthe known art on a sleeve of elastomeric material identical to the onespecified above.

Referring to the conventional cycle in an autoclave as shown in FIG. 1b,the centripetal compression on the sleeve is obtained for example byadmitting water overheated to a temperature of 164° C. and at a pressureof 18 bar as shown by curve "N", into an elastomeric plenum chamberconventionally provided in the autoclave and externally surrounding thesleeve fitted on the drum. These conditions are the same over the wholeoperating cycle of the autoclave which cycle is of a duration ofapproximately 16 minutes.

Still, with reference to FIG. 1b, the curve marked by shows thevariation in time of the pressure of the steam admitted into the drumcarrying the sleeve, according to known procedures. In a starting step,lasting about three minutes, as shown by the initial length K' of curveK, the steam pressure in the drum is maintained at a value of about 2.2bar at a temperature of 134° C., in order to cause plasticization of theelastomeric material. In a subsequent cross-linking step, shown bylength "K"" of curve K, the steam pressure within the drum is raised upto about 6 bar, at a temperature of 164° C. and these conditions aremaintained over the remaining 13 minutes of the operating cycle, atwhich time the cross-linking of the elastomeric material comes to anend.

As mentioned above, according to the known art, final formation of teeth3 on the inside circumferential surface of the sleeve occurs, as well asthe cross-linking of the elastomeric material 2.

However, unlike the above procedures, in the preforming step carried outin the example shown in FIG. 1a the operating cycle in the autoclave isreduced to about 6 minutes during which steam, admitted into the drum,is maintained at a pressure of 1.2 bar at a temperature of 120° C., asshown by curve "Z". The overheated water introduced into the plenumchamber surrounding the sleeve is maintained at a pressure of about 18bar and at a temperature of 164° C., as shown by curve "X".

It is noted that the important reduction in the time of the operatingcycle in the autoclave together with the small reduction in thetreatment temperatures and steam pressure within the preforming drumcauses the preforming step to occur without any risk of giving rise tocross-linking the elastomeric material 2.

The important reduction in time of the operating cycle in the autoclave,due to possible temperature differences in the various areas of theautoclave or for other reasons, leads to the formation of projectionsthat can at least partly correspond to the final shape of teeth 3, asintentionally emphasized in FIGS. 3 and 4. In particular, taking intoaccount the fact that the sleeve is disposed in the autoclave accordingto a vertical axis, teeth 3 can show a gradual reduction in height alongthe longitudinal extension of the sleeve towards the lower part thereof,but they will in all event exhibit the respective base walls 5a (FIG. 4)mutually levelled adjacent the cord layer 1.

Advantageously, in the process of the invention, for reasons made clearbelow, the presence of possible projections which are different from oneanother and from the final form of the teeth 3 do not give rise to anyqualitative deficiency in the finished product.

In fact it has been found that in order to achieve a final producthaving satisfactory characteristics it is sufficient that the depth ofgrooves 5 denoted "h" in FIG. 4, be at least equal to 1/3 of the overallheight "H" of the tooth 3 in the finished product. It is also importantto point out that preferably the surface length of the transverseprofile of each projection 3a defined between two contiguous grooves 5must at least correspond to 1/2 of the surface length of the transverseprofile of each individual tooth 3.

It has also been found that the above parameters are complied with if inthe inside of the autoclave the administration of heat to the sleeve iscarried out over a period of time included between 1/4 and 1/2 of thetime needed for causing the complete cross-linking of the elastomericmaterial at temperature conditions according to which the heatadministration occurs. In other words, it is pointed out that even ifthe temperature and pressure conditions are kept substantially unchangedas compared to the autoclave cycle of the known art, the duration of theoperating cycle for achieving the preforming cycle of the invention isreduced to between 1/6 and 1/2 of the duration of the conventionaloperating cycle in an autoclave.

Alternatively, the administration of heat to the sleeve can be carriedout by submitting the latter to temperatures ranging from 1/2 to 4/5 ofthe value required for achieving the complete cross-linking of theelastomeric material, over a period of time corresponding to theconventional duration of the administration of heat. In other words, theduration of the preforming step can even be as long as the duration ofthe known operating cycle, in which case in order to preventcross-linking in the elastomeric material, the operating temperatureswithin the preforming drum and in the autoclave plenum chamber shouldconveniently be reduced to a value in the range of 2/3 to 4/5 of thetemperatures detectable in a conventional autoclave cycle.

Obviously, depending on the different requirements within the abovespecified limits, it will be possible to select any time and temperaturecombination adapted to produce sufficiently deep hollows 5 withoutcausing the elastomeric material to cross-link.

In a preferred solution the centripetal compression in the preformingstep should be included between 15 bar and 21 bar, the residence time inthe autoclave between 3 and 10 minutes and the temperature in thepreforming drum, that is within the sleeve, between 100° C. and 140° C.,and the temperature on the outside of said sleeve ranging from 50° C. to205° C.

The absence of cross-linking in the elastomeric material submitted tothe preforming step can be confirmed by examining the rheometricfeatures of a sample of this material, and comparing such features withthe rheometric features detectable on a coupon of identical materialproduced under the same test conditions that has not been submitted tothe preforming cycle in the autoclave.

Diagrams shown in FIGS. 2a and 2b show the results achieved by carryingout a test, known to those skilled in the art as the "Monsanto-test", ona sample of elastomeric material previously submitted to a preformingcycle and a sample of the same raw material not submitted to said cycle,respectively.

For the sake of completeness, it is pointed out that the "Monsanto test"substantially consists in putting an elastomeric sample, of 5 cmdiameter and 3 mm thickness, in a chamber heated to a controlledtemperature, in this case corresponding to 185° C., and detecting thevariation in time of torque "C" (to be measured in Newton·meter)necessary to cause the angular oscillation (according to an angle of 1°to 3° in absolute value) of a disk rotatably housed within said chamber.

The increase of the torque value in time, detectable from graphs inFIGS. 2a and 2b, is the cross-linking index taking place in theelastomeric material by effect of its standing at high temperature andwill be stabilized when the cross-linking has been completed.

As can be seen, the graphs depicted in FIGS. 2a and 2b, are practicallyidentical, which means that the elastomeric material sample submitted tothe cycle corresponding to the preforming step is still in a raw state,in that it exhibits the same behavior as the raw material sample thathas not yet been submitted to any treatment in the autoclave.

In principle, the elastomeric material 2 of the preformed sleeve ispreferably provided to exhibit, after a test in a Mooney viscosimetercarried out in accordance with ASTM 1646-80 standards, a viscosityincrease lower than 10%.

It is also noted that in the described example the hardness of theelastomeric material after the preforming step is not measurable becausethe material is not vulcanized, whereas the hardness of the samematerial on the finished belt has a value ranging from 60 to 90 Shore A.

In accordance with the process of the invention the preformed sleeve issubsequently submitted to a cutting step following a helical-extensioncutting line, the pitch of which is preferably the same as, or amultiple of the pitch according to which the wrapping of the reinforcingcord layer 1 on the preforming drum has been previously carried out, inorder to prevent, as much as possible, cutting the reinforcing cordsalong their length.

Preferably the cutting is carried out by removing the preformed sleevefrom the performing drum and placing it on a rubber drum in which thelongitudinal axis of the sleeve is parallel to the axis of rotation ofthe rubber drum. The sleeve is then helically cut. Following thishelical cutting step a semifinished product is obtained in the form of acontinuous strip 7 (FIG. 3) of predetermined width and coincident withthe pitch of the helical-cutting line, in which grooves 5 producedduring the preforming step extend in the transverse direction. Helicalcutting is more completely described in U.S. Pat. No. 4,448,621 thedisclosure of which is hereby incorporated by reference.

As diagrammatically shown in FIG. 3, the semifinished product in theform of a continuous strip 7 is then wrapped over at least two spacedapart grooved wrapping rollers 8, 9 having their axis of rotationparallel to one another and positioned apart from each other accordingto a predetermined distance measured from axis to axis of the respectiverollers which distance depends on the circumferential length to be givento the finished belts. The grooves of the rollers are parallel withrespect to axis of the rollers. In greater detail, the wrapping of thesemifinished product 7 obtained by preferably driving in rotationrollers 8, 9 is carried out helically according to a pitch correspondingto the width of the semifinished product itself, so as to produce anannular element 10 exhibiting at least the same width as one of thebelts to be obtained.

Advantageously, during the wrapping of the semifinished product 7 themutual alignment of the transverse grooves 5 present on the individualloops 10a formed from the semifinished product, is also achieved. Thisalignment results from the engagement of grooves 5 on alignment teeth8a, 9a which teeth extend longitudinally on each of the wrapping rollers8, 9 and which are mutually spaced apart a distance corresponding to thetoothing pitch "P". The alignment teeth 8a, 9a have a heightcorresponding to, or greater than the depth "h" of grooves 5. In thisway the alignment teeth 8a, 9a can act on the base portion 5a of eachindividual groove 5, so that the individual loops 10a formed from thesemifinished product 7 wrapped on rollers 8, 9 are perfectly levelled.

Advantageously, the engagement of the transverse grooves 5 on thealignment teeth 8a, 9a also enables the perfect alignment of the groovesand the individual loops 10a to be achieved in the wrapping step withouttensioning the semifinished product 7. Thus, any risk of deforming theelastomeric material 2, which is still in the raw state, is eliminated.

The annular element 10 obtained from the wrapping step is subsequentlytrued up by means of grooves 5 and submitted to a pressing step betweena molding matrix 11 and an opposing mating mold member 12 which membersare pressed together or moved close to each other.

As shown in FIG. 4, flat contact surface 12a of molding element 12 actson an outer surface 10c of the annular element 10, whereas the moldingmatrix 11 acts on an inner surface 10b of the annular element by ashaped surface 11a thereof. This shaped surface 11a has ridges 13matching the shape of the transverse grooves 5 spaced out by recessesmatching the shape of the outline of the individual teeth 3 to beobtained.

Following the pressing together of matrix 11 and mold 12, the finaltrueing up of the respectively aligned grooves 5 belonging to thedifferent loops 10a of the annular element 10 is advantageouslyobtained. Simultaneously, the elastomeric material 2 located at theprojections 3a is urged into the recesses 14 of matrix 11 thereby surelydetermining the exact formation of teeth 3.

Concurrently with the pressing step, cross-linking of the elastomericmaterial 2 is carried out by heating matrix 11 and opposite mold 12, ina conventional manner so as to cause the final mutual bonding of loops10a and structural stabilization of the belt being worked.

As suggested from FIG. 4, the pressing step and the relatedcross-linking step are carried out according to successive stages, toeach of which the execution of said steps on a portion of predeterminedlength of the annular element 10 corresponds, which length in turncorresponds to the longitudinal extension of matrix 11. In particular, alongitudinal stepping movement is provided to be transmitted to theannular element 10 fitted on rollers of parallel axes, in synchronismwith the alternate movement imparted to the matrix 11 and/or oppositemold 12 for pressing and simultaneous cross-linking on the individualportions of the annular element.

The trueing up of grooves 5 ensures the elimination of possiblemisalignments present between the grooves and/or projections 3a afterthe wrapping step.

Still in accordance with the present invention, during the pressing stepa covering fabric 15 previously interposed between the molding matrix 11and the annular element itself is preferably applied during the pressingstep to the inner surface 10b of the annular element 10. This coveringfabric has the function of increasing the mechanical strength of teeth 3and the wear resistance of the obtained belt.

Provision may be made for the pressing step and other steps of theprocess related thereto to be carried out directly on the annularelement 10 still fitted on the wrapping rollers 8, 9 when the wrappingstep is over. In this case the covering fabric 15 should be preferablydisposed around the wrapping rollers 8, 9 before or after the executionof the wrapping step of the semifinished product in the form of a strip7. The covering fabric 15 will be thus disposed intermediate thewrapping rollers 8, 9 and the annular element 10 and will be finallyfastened to the annular element as a result of the pressing andcross-linking step.

The preliminary application of the covering fabric 15 during thewrapping step can also be exploited for the purpose of achieving amutual presetting of the loops 10a forming the annular element 10 shouldthe annular element be disengaged from the wrapping rollers 8, 9 and betransferred to another work station designed to carry out the pressingand cross-linking steps.

Alternatively, the mutual presetting of loops 10a can be obtainedthrough the application of at least a coating sheet of plastic material,not shown, to the outer surface 10c of the annular element 10, stillfitted on the wrapping rollers 8, 9. This coating sheet may beoptionally eliminated during the following rasping step executed inknown and conventional manner on the belt back.

Should the annular element 10 exhibit substantially the same width asthat of each individual belt, after the pressing and cross-linking stepa trimming step may be executed on the side edges of the annular elementso as to give the same a perfectly parallel extension and define theexact belt width.

This trimming operation is also necessary because, in order to be sureto obtain a tooth of the desired form, the elastomeric material of theannular element is always in excess and thus there is the formation ofloose threads at the edges of the mould after its being closed with themolding matrix (FIG. 4).

Alternatively, should the width of the annular element 10 be a multipleof the width of each individual belt, before or after the pressing andcross-linking operations a final-cutting step can be executed on theannular element following circumferential lines spaced apart from eachother a distance equal to the width of the belts to be produced.

Belts manufactured following the process in question, as a result of thehelical cut carried out on the sleeve and the subsequent helicalwrapping for producing the annular element 10, will exhibit therespective textile reinforcing layers 1 and coating fabric 4 eachstructured in the form of a continuous strip forming loops disposed inside-by-side relation and mating at the respective opposite edges.

In addition, belts made in accordance with the invention may be providedwith the covering fabric 15 disposed on the respective inner surfacethereof exhibiting the teeth 3 and structured in the form of acontinuous strip of the same width as the belt.

Another peculiar feature of belts made in accordance with the inventionresides in the high ultimate tensile strength they offer. Actually, ithas been found that the ultimate tensile strength of the belts of theinvention is much higher than 50% of the ultimate tensile strength foundon belts made of the same materials and obtained from a circumferentialcutting of a sleeve directly molded and vulcanized in the autoclavefollowing the known art. More particularly, the tensile strength of thebelts of the invention can easily exceed 85% of the tensile strengthfound on junction-free belts of the above type.

The slight reduction in the tensile strength of the belts of theinvention when compared to the belts obtained from the circumferentialcutting of a molded and cross-linked sleeve, is only due to the helicalarrangement of the textile fibers forming the layer 1, owing to thehelical wrapping carried out on rollers 8 and 9. At all events thestrength values obtained by the invention represent an importantimprovement over conventional belts obtained by butting the oppositeends of a strip length previously cut to size. In these belts, in fact,the ultimate tensile strength does not generally exceed 35% of theultimate tensile strength detectable on junction-free belts.

During the pressing step of the mold members 11 and 12, the covering 15is unrolled from a drum and applied to the toothing of the beltsubstantially as already explained for the plurality of layers appliedto the back of the annular element 10.

Advantageously, during the pressing step the covering 15 avoids anyleakage of elastomeric material to the outside allowing for the finishedbelt the appropriate meshing with the surface of the pulley of thetransmission.

Furthermore, the covering 15 provides during the pressing step acontrolled and uniform flux or elastomeric material between the recessesof the matrix 11.

According to an example, the mutual presetting of the loops 10a of theannular element 10 can be obtained by applying a plurality of pincerswhich press the two opposite surfaces of one portion of the annularelement 10.

The plurality of pincers is used to transport the annular element 10 tothe molding elements and the pincers may be used to maintain a portionof the annular element 10 between the matrix 11 and the mold 12.

Further as already cited, according to the most preferred method of theinvention, a quantity of elastomeric material which is preformed in theautoclave is less than that required to completely shape the teeth ofthe belt or to reproduce a finished belt.

For example, the quantity of elastomer used for the sleeve introduced inthe autoclave for the preforming cycle may be that quantity needed toshape a belt whose thickness between the back of the belt and the top ofthe teeth is 2/3 of the thickness desired for the finished belt.

Therefore, prior to cross-linking the preformed belt a plurality oflayers of non-cured or noncross-linked elastomeric material reciprocallyoverlapped, are applied around the outermost surface of the annularelement 10 covering all the adjacent turns of the strip 7.

Preferably, the plurality of layers forming a single foil are unrolledfrom a drum placed at the right side of FIG. 4.

To complete a belt, the first edge of the said plurality of layers isunrolled from the corresponding drum and a length thereof is applied tothe first portion of the annular element 10 to be pressed between thematrix 11 and the mold 12.

Successively, after the pressing and curing of the first portion of thebelt, the mold 12 and the matrix 11 are separated and further pieces orlengths of the said plurality of layers are unrolled from the drum andplaced onto a non-cured, not yet pressed sections of the belt which arethen press-heated cross-linked.

The number of layers selected is determine, after the pressing step, sothat the desired thickness of the finished belt between its back and thetop of the teeth can be obtained.

Preferably the composition of the elastomer material of the sleeve inthe preforming cycle and that of the said plurality of layers is thesame.

Advantageously, during the pressing step, the plurality of layersphysically connects all the adjacent turns of the strip 7 determining asingle annular element.

Further, the said plurality of layers fills in any voids ordiscontinuities that could exist between adjacent turns of the strip 7and determine uniformity of thickness for the whole length and width ofthe finished belt.

Still advantageously, the plurality of layers forms a resistantstructure opposed to any reciprocal sliding between adjacent turns ofthe strip 7 when the finished belt is associated with two pulleys whoseaxis are not aligned in the same direction.

Preferably, the method comprises the step of forming an inner coatingfabric 4 of reduced thickness for the sleeve introduced in the autoclaveand a covering fabric 15 placed, before the pressing step, on the wholewidth on the inner surface of the belt.

The total thickness of the fabric 4 and the covering 15 must bedetermined from the finished belt, after the pressing step, a thicknessbetween the cords 1 and the center of the groove, as required for theappropriate meshing of the belt with the pulleys of the transmission.

More specifically, the thickness of the finished belt, measured from theplane of the longitudinal cords 1 to the center of the groove betweenadjacent teeth of the belt, must correspond to the value of the knownparameter "a" defined as the PDL (Pitch Difference length).

For example, said parameter "a" has a value of 0.685 mm for a belthaving the following geometrical parameters:

pitch=8 mm

height between the land area and the top of the tooth=3.2 mm

total thickness=5.2 mm

pressure angle=16°

root of the tooth a 5.50 mm

In the same example one of the pulleys of the transmission has thefollowing geometrical parameters:

Teeth=30

Diameter of the pitch line=76.39 mm

Diameter of the outer circumference of the pulley is 76.39-2×"a" whichis calculated as follows: 76.39-2×0.685=75.02

The fabric 4 and the covering 15 may have following characteristics:

Covering 15.

Material=for example nylon.

Weight=between 180 and 300 gr/mq and more preferably between 220 and 250gr/mq

Thickness=between 0.75 and 0.85 mm

Elasticity=between 7% and 15%.

The elasticity is measured applying a tensile stress of 2 kg to a sampleof fabric having the length of one meter and a width of 10 centimeter.

Fabric 4.

Thickness of about 0.25 and 0.30 mm.

Therefore the present invention achieves important advantages ascompared to the known art.

It will be recognized, among other things, that based on knowledge inthis field, the irregularity of grooves 5 and surface projections 3aobtained in the preforming step would be interpreted as an adversefactor affecting the satisfactory manufacture of a finished product.

On the contrary, surprisingly the invention succeeds in advantageouslyexploiting the presence of said hollows, even if of irregular form, forachieving the perfect alignment of the individual loops 10a and surfaceprojections 3a in the following wrapping and pressing steps, makingthereby possible the accomplishment of a final product offeringexcellent qualitative features.

In particular, circular, trapezoidal and parabolic-sided teeth, and ingeneral teeth of any form, can be obtained.

In addition it is possible on demand to convert a projection of theannular element for example of circular form into one in which the toothsides are for example of parabolic or hyperbolic form by merelydisposing the same type of annular element between molds of the desiredconfiguration.

Obviously modifications and variations may be made to the invention asconceived, all of them falling within the scope of the inventive ideacharacterizing it; for example it is possible to achieve belts having asingle fabric on the toothing, of the same width as that of the beltitself.

We claim:
 1. A toothed belt of elastomeric material, comprising:at leasta reinforced cord layer of annular configuration; at least a layer ofelastomeric material incorporating said reinforced cord layer andsupporting a plurality of spaced apart teeth extending radially inwardlyrelative to the circumferential extension of the belt; said reinforcedcord layer structured in the form of a continuous strip helicallywrapped in several loops, said strips disposed in a side-by-siderelation and mating at respective opposite edges; said toothed beltfurther comprising at least a covering fabric applied to saidelastomeric layer, said covering fabric being structured in the form ofa continuous strip having the same width as the belt.
 2. The toothedbelt of claim 1 wherein said teeth are spaced equidistant apartaccording to a predetermined toothing pitch.
 3. The toothed belt ofclaim 1 wherein said covering fabric is applied to the surface of theelastomeric layer having thereon said spaced apart radially inwardlyextending teeth.
 4. A belt according to claim 1 further comprising atleast a coating fabric applied to the surface of the elastomericmaterial supporting said teeth, said coating fabric being structured inthe form of a continuous strip wrapped in several side-by-side loops andmating at the respective opposite edges.
 5. A belt comprising an annularelement having a plurality of teeth spaced apart by grooves andincorporating longitudinally extending reinforcing cords, said beltbeing manufactured in respective steps comprising: helically wrapping astrip of non-cross-linked elastomeric material incorporatinglongitudinally extending reinforced cords in a plurality of loopsdisposed in mutual side-by-side relation producing said annular element,said elastomeric material having teeth partially shaped thereon;moldingthe annular element by pressing the annular element between a matrix andan opposing mold member and curing the annular element to impart a finalshape to said teeth wherein a fabric having the same width of saidplurality of loops disposed in mutual side-by-side relation is appliedto the plurality of teeth and grooves during molding such that thefinished thickness of the belt, measured from the plane of thelongitudinal cords to the center of the grooves, corresponds to apredetermined value for obtaining the appropriate meshing of the beltwith a toothed pulley.
 6. A belt according to claim 5 further comprisingat least a coating fabric applied to the inner surface of theelastomeric material, said coating fabric being structured in the formof a continuous strip wrapped in several side-by-side loops and matingat the respective opposite edges.